Hot water heater with in-tank heat exchanger tube

ABSTRACT

The invention relates to a hot water heater that includes a tank, one or more heating elements, one or more thermostats and one or more heater exchanger tubes. The tank has a water outlet and one or more water inlets. The one or more heating elements extend within the tank. The one or more thermostats function to control the energy applied to the one or more heating elements. The one or more heater exchanger tubes are positioned within the tank. Each heater exchanger tube has a first end with a first opening and a second end with a second opening and defines a channel between the two openings. The second opening in the channel opens into the tank. Each heater exchanger tube surrounds at least a portion of one heating element. The water inlet includes an opening into the heater exchanger tube for water to enter the heater exchanger tube.

TECHNICAL FIELD

The field of the invention generally relates to electric hot water heaters with an in-tank heater exchanger tube and methods of controlling the energy usage of electric hot water heaters containing an in-tank heater exchanger tube.

BACKGROUND

Every household and many businesses require hot water for everyday use. These hot water consumers typically rely on conventional storage water heaters to store and constantly heat water for production upon demand.

A variety of fuel options are available for conventional storage water heaters, including electricity, natural gas, oil, and propane. Ranging in size from 20 to 80 gallons (75.7 to 302.8 liters), storage water heaters remain the most popular type for residential heating needs in the United States. A storage heater operates by releasing hot water from the top of the tank when the hot water tap is turned on. To replace that hot water, cold water enters the bottom of the tank, ensuring that the tank is always full.

Because the water is constantly heated in the tank, energy can be wasted even when no faucet is on. This is called standby heat loss. It is possible to completely eliminate standby heat losses from the tank and reduce energy consumption 20% to 30% with demand (tankless) water heaters, which do not have storage tanks. Cold water travels through a pipe into the unit, and either a gas burner or an electric element heats the water only when needed.

SUMMARY

In one general aspect, a hot water heater includes a tank, one or more heating elements, one or more thermostats and one or more heater exchanger tubes. The tank has a water outlet and one or more water inlets. The one or more heating elements extend within the tank. The one or more thermostats function to control the energy applied to the one or more heating elements. The one or more heater exchanger tubes are positioned within the tank. Each heater exchanger tube has a first end with a first opening and a second end with a second opening and defines a channel between the two openings. The second opening in the channel opens into the tank. Each heater exchanger tube surrounds at least a portion of one heating element. The water inlet includes an opening into the heater exchanger tube for water to enter the heater exchanger tube.

Embodiments of the hot water heater may include one or more of the following features. For example, the heater exchanger tube and the heating element may be collinear with the heating element positioned within the heater exchanger tube. The heating element may be generally of a similar length as the heater exchanger tube, shorter in length than the heater exchanger tube, or longer in length than the heater exchanger tube.

The heater exchanger tube may be made up of a fitting and a tube with the tube extending from the fitting. The heater exchanger tube may be made of copper. The heater exchanger tube may include one or more fins extending from an outer surface of the heater exchanger tube. The heater exchanger tube may include one or more baffles extending from an inner surface of the heater exchanger tube into the channel of the heater exchanger tube.

The details of various embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will be apparent from the description, the drawings, and the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective side view of a conventional electric hot water heater with a cutaway section showing the interior of the tank.

FIG. 2 is a side view of a hot water heater having a water inlet that passes water into the tank through a heater exchanger tube.

FIG. 3 is a side view of the hot water heater of FIG. 1 with a cutaway section showing the interior of the tank.

FIG. 4 is a perspective side view of the hot water heater of FIG. 1 with a cutaway section showing the heater exchanger tube encasing the heating element within the tank.

FIG. 5 is an enlarged perspective side view of the hot water heater of FIG. 4 with a cutaway section showing a cutaway view of the heater exchanger tube encasing the heating element within the tank.

FIGS. 6-8 are side, end and perspective view of the heater exchanger tube of the hot water heater of FIG. 2.

FIG. 9 is a cross-sectional side view of the heater exchanger tube of FIG. 6.

FIG. 10 is a cross-sectional side view of a heater exchanger tube having outer heating fins and inner baffles.

DETAILED DESCRIPTION

The inventor has developed a heater exchanger tube that can be used in new hot water heaters or retrofit into conventional hot water heaters. The heater exchanger tube surrounds or encases the heating element that conventionally is positioned within the tank of hot water heater. In this manner, cold water that enters the tank passes through the heater exchanger tube around the heating element to effect an increased transfer of heat from the heating element to the water, thereby providing a faster recovery of the cold water to the desired water temperature within the tank.

Referring to FIG. 1, a conventional electric, storage tank type hot water heater 10 includes a tank 15; one or more dip tubes 20 a, 20 b; one or more thermostats 25 a, 25 b; one or more heating elements 30 a, 30 b; a sacrificial anode rod 35; a shut off valve 40, a water outlet 45, and a drain valve 50. In use, cold water passes through the shut off valve 40 into the dip tubes 20 a, 20 b. The water enters the dip tubes in the tank 15 at the top of the tank and pass out of the dip tubes in the bottom region of the tank. The thermostats 25 a, 25 b are used to adjust the water temperature by controlling the electrical energy that passes through the heating elements 30 a, 30 b. The heating elements heat the water and the heated water passes out of the tank 15 through a water outlet 45. The sacrificial anode tube 35 extends into the tank, is typically a steel core with a magnesium or aluminum coating, and is used to help retard corrosion of the hot water heater system. The drain valve 50 is used to drain the tank to remove, for example sediments in the tank, and permit work to be done on the tank, such as replacing heating elements.

When cold water enters the conventional hot water heater 10, the cold water is mixed with the heated water. Because the entering cold water is mixed with the heated water in the bottom region of the tank, there will be a temperature gradient over the height of the tank with warmer water being at the top of the tank and cooler water being at the bottom of the tank. After, for example, an individual takes a shower, there will be a period during which the mixture of cold and hot water in the tank is heated to the set point of the thermostat. This period is called the recovery time. During the recovery time, the heating element is heating the water adjacent to the element and the water further away will gradually rise in temperature.

Referring to FIGS. 2-5, an improved electric, storage tank hot water heater 100 includes a tank 115; an outer water inlet tube 120; one or more thermostats 125; one or more heating elements 130; a sacrificial anode rod (not shown); a shut off valve (not shown); a water outlet 145; a drain valve (not shown); a heater exchanger tube 150; and a pressure relief valve 155. The outer water inlet tube 120 has an outlet into the tank 115 through the heater exchanger tube 150. The heater exchanger tube 150 and the heating element 130 are collinear with the heating element positioned within the heater exchanger tube and generally being of a similar length as the heater exchanger tube. The configuration of the heater exchanger tube and heating element are such that cold water that enters the tank 115 must first pass over the heating element. In this manner the cold water, which typically is at 50-55° F., is in contact with the heating element for a longer period of time before leaving the heater exchanger tube and entering the body of the tank. This configuration quickly heats the water that enters the tank through the heater tube.

Referring to FIGS. 6-9, in one embodiment the heater exchanger tube is 150 is a copper tube 170 that extends from a copper fitting 175. The copper fitting 175 may be in the form of a nut having a channel 177 along its length with an opening 185 at one end and the copper tube 170 at the other end. The copper tube has a channel 178 that is collinear with the channel 177 in the fitting 175 and terminates in an opening 183. The copper fitting 175 also includes a channel 179 through the side wall of the fitting and with openings on the side wall of the fitting and on the inside surface of the fitting that is contact with the channel through the length of the nut. A short copper tube 180 extends from the side wall of the nut and is used to connect to a water line to supply cold water to the heater.

The copper fitting 175 includes a threaded section 190 on the inner surface that defines the channel 177. The threaded section 190 is configured to receive a heating element assembly. The heating element assembly includes the heating element 130.

When the heating element assembly is mounted within the heater exchanger tube 150, the heating element 130 extends the length of the tube 170. Although the figures illustrate the heating element 130 and tube 170 being of similar lengths, the tube 170 may extend beyond the heating element 130 or the heating element 130 may extend beyond the heater exchanger tube 170.

The heater exchanger tube is preferably made of copper. Copper provides quick heat dissipation of the heat generated by the heating element. For example, as water is drawn from the tank, the heating element will heat the cold inflowing water as it enters the heater exchanger tube. Once the demand for hot water ceases, the water in the tank may not yet be at the temperature of the set point of the thermistor. In such a condition the heating element will continue to heat the water in the tank. Although water will no longer be passing through the heater exchanger tube, the heating element will continue to generate heat and heat the water within the tube. As the water within the tube is heated, the heater exchanger tube will become heated and can conduct heat to water surrounding the outside of the tube. In this manner, the water in the tank is heated. In effect, with the heater exchanger tube of the present invention, the combination of the heating element, heater exchanger tube and hot water within the heater exchanger tube function together as a heat source. This heat source advantageously has a surface area in contact with the water in the tank that is greater than the surface area in contact with the water in the tank of a conventional hot water heater using a heating element but not having a heater exchanger tube.

Other materials may be used in place of the copper tube. The material selected for the heater exchanger tube must not corrode and must dissipate heat. For example, one suitable metal is aluminum.

The heater exchanger tube assembly 150 and heater exchanger tube 170 may be part of a new electric hot water heater or retrofit to an existing electric hot water heater. When used in a retrofit application, the conventional heating element first is removed and the heater exchanger tube assembly 150 is inserted into the opening in the tank where the heating element 125 was originally mounted. Next, the heating element 125 is mounted into the copper fitting 175 of the heater exchanger tube assembly 150 ensuring that the heating element is positioned within the channel 178 of the tube. It should be understood that the length of the tube can be adjusted to be the same length as, or longer or shorter than, the heating element. Next, the cold water inlet of the convention hot water heater is sealed to prevent water leakage and the water piping connected to the tube 180 of the copper fitting 175.

If the hot water heater has multiple heating elements, the above procedure is applied to each heating element. In this manner, a hot water heater with multiple heating elements will have each heating element encased within a heater exchanger tube such that all cold water entering the hot water heater will be heated in the heater exchanger tube prior to being dispersed within the tank.

A typical electric hot water heater has a 4500 watt heater rating and when used conventionally for taking a shower has a one gallon per minute draw of hot water and therefore will have a cold water draw of one gallon per minute into the tank of water at 55° F. that must be raised to 140° F. The time that will be taken to raise the temperature of the water in the tank to 140° F. will be a function of the temperature of the water entering the tank. The inventor has determined that under the conditions above (i.e., electric hot water heater with a 4500 watt heater rating and a draw of one gallon per minute of water at 55° F. that must be raised to 140° F.), the hot water heater using the heater exchanger tube 170 will heat the water by approximately 30° F. Therefore, water entering the heater exchanger tube at 55° F. will be raised to approximately 85° F. before it leaves the heater exchanger tube and enters the main body of the tank. Because the time necessary to raise the temperature of the water in the tank to the set point will be a function of the temperature of the water entering the tank, heating the water to approximately 85° F. will reduce that time.

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It should be understood that the heater exchanger tube provides at least two advantages as compared to conventional electric hot water heaters. First, there is an increase in proximity of the cold water to the heating element which raises the temperature of the water entering the tank. Second, there is an increase in surface area of heating surface exposed to the water within the tank. Each of these advantages improve the efficiency of the electric hot water heater.

To further provide advantages to the electric hot water heater, the heater exchanger tube may be modified from that of FIGS. 2-9 to (a) increase the residence time of the water within the heater exchanger tube; (b) increase the turbulence of the water within the heater exchanger tube; and (c) increase the surface area of the heating surface exposed to water within the tank. Referring to FIG. 10, to accomplish one or more of these objectives, the heater exchanger tube can include baffles 205 extending into the inside channel 178 or fins 210 extending from the outside of the tube. The baffles 205 within the channel 178 cause turbulence of the water and will improve heat transfer between the heating element and the water. By diverting the flow around the baffles 205, the water will spend more time within the heater exchanger tube and thereby increase the residence time. In this manner, the water will remain in contact with the heating element longer. It should be understood that other elements in place of or in addition to the baffles may be used to cause turbulence of the water in the heater exchanger tube and/or increase the residence time of the water in the heater exchanger tube. Further, a variety of arrangements of the baffles may be used.

The fins 210 will cause heat to radiate from the heater exchanger tube by increasing the heating surface exposed to water in the tank. Although this source of heating is less important when cold water is flowing through the heater exchanger tube, once the draw of hot water has ceased and the heating element is heating the water to the set point, the fins will more rapidly transfer heat to the water in the tank. It should be understood that the heating fins 210 may be of a variety of sizes (e.g., length and thickness) and spacings to optimize heat dissipation from the heater exchanger tube.

While several particular forms of the invention have been illustrated and described, it will be apparent that various modifications and combinations of the invention detailed in the text and drawings can be made without departing from the spirit and scope of the invention. For example, references to materials of construction, methods of construction, specific dimensions, shapes, utilities or applications are also not intended to be limiting in any manner and other materials and dimensions could be substituted and remain within the spirit and scope of the invention. Similarly, although FIGS. 2-5 illustrates the hot water heater 100 having only one heating elements and heater exchanger tube, additional heating elements may be used depending upon the application. Accordingly, it is not intended that the invention be limited, except as by the appended 

What is claimed is:
 1. A hot water heater comprising: a tank having a water outlet and one or more water inlets; one or more heating elements extending within the tank; one or more thermostats to control the energy applied to the one or more heating elements; and one or more heater exchanger tubes being positioned within the tank, each heater exchanger tube having a first end with a first opening and a second end with a second opening and defining a channel between the two openings, wherein each heater exchanger tube surrounds at least a portion of one heating element, and the second opening in the channel opens into the tank, and wherein the water inlet comprises an opening into the heater exchanger tube for water to enter the heater exchanger tube.
 2. The hot water heater of claim 1, wherein the heater exchanger tube and the heating element are collinear with the heating element positioned within the heater exchanger tube.
 3. The hot water heater of claim 2, wherein the heating element is generally of a similar length as the heater exchanger tube.
 4. The hot water heater of claim 2, wherein the heating element is shorter in length than the heater exchanger tube.
 5. The hot water heater of claim 2, wherein the heating element is longer in length than the heater exchanger tube.
 6. The hot water heater of claim 1, wherein the heater exchanger tube comprises a fitting and a tube, wherein the tube extends from the fitting.
 7. The hot water heater of claim 1, wherein the heater exchanger tube is made of copper.
 8. The hot water heater of claim 1, wherein the heater exchanger tube includes one or more fins extending from an outer surface of the heater exchanger tube.
 9. The hot water heater of claim 1, wherein the heater exchanger tube includes one or more baffles extending from an inner surface of the heater exchanger tube into the channel of the heater exchanger tube. 